1. Field of Invention
The invention is in the field of cable-like elements in protective tubes. More particularly the invention concerns a method for inserting a cable-like element in an elongate tube-like member which is in a coiled state in or on a holder, using the fluid drag of a medium flowing through the tube-like member in the direction of insertion along the cable-like element already inserted in the tube-like member, and subjecting the holder together with the tube to a periodic movement including a vertical component.
2. Prior Art
Inserting cable-like elements, such as optical cables or electric wire cables, in protective tubes using the drag of a fluid flowing along the cable-like element in the tube is a generally known technique. Not only for installing cables in pre-laid tubes or ducts, but also for the manufacturing of cables, especially optical fibre cables. Using the fluid drag of a gaseous medium for installing flexible fibre bundles in small bores has been disclosed in EP-A-0108590. In addition, using the fluid drag of a gaseous medium for installing cables in tubes has been disclosed in EP-A-0292037. Further the insertion of an optical fiber in a metal tube in a coiled state by using the drag of a liquid as a production step in manufacturing an optical fibre cable is known from U.S. Pat. No. 4,332,436.
Prefab (factory) installation of a cable in a tube is in many cases less expensive than installation in the field. Extrusion of a tube around a cable is one way to do this. In this it is not always possible to avoid unwanted effects, such as tacking of the tube to the cable. Insertion of a cable in a tube is another way. Therein it will be practical to keep the tube on the reel. Insertion by means of pulling is not suitable, since a tube on a reel makes up an extremely tortuous path along which the cable should be pulled. Consequently the effect of fluid drag of a gaseous or a liquid medium may be used, possibly in combination with pushing. However the insertion lengths which can thus be reached over such a tortuous path are rather limited. To be a suitable manufacturing step insertion lengths of one kilometer and more should be achieved.
A much different technique for inserting a cable-like element in a tube coiled round a reel is known from EP-A-0091717 and EP-A-0279006. According to this known technique the reel is, with its axis vertically, subjected to a periodic movement, in which the tube returns periodically to its initial position. According to EP-A-0091717 the element moves in the tube, i.e. a bore or a channel in a carrier member such as a ribbon, as a result of the periodic movement and its mass of inertia. Periodic movements which are vibratory and/or pulsatory or shaking, are disclosed, in which the, preferably harmonic, vibrating movement has a relative small inclination angle to the longitudinal direction of the tube. Reference EP-A-0279006 discloses a similar technique in which the periodic movement is a so called helical vibration, i.e. a movement with a small vertical component and a longer longitudinal component in a screw-thread manner. Thus in both of these known insertion methods the cable-like element is vibrated forwardly along the curved path of the tube. Therein the longitudinal component of the vibration may provide a small advancing force, whereas simultaneously the vertical component may provide a momentary reduction of the friction between the cable-like element and the inner surface of the tube. In order to be effective, however, the vibrations should have a relative large frequency and a relative small amplitude. Consequently it is necessary that the tubes are well fixed to the reel, which needs special techniques and may cause extra labour, e.g. extra spooling of the tube on a special reel. Moreover a minimum diameter of the tube with respect to the diameter of the cable-like element is required for these known methods to be effective.
EP-A-0354295 describes a technique similar as known from EP-A-0279006, in which additionally during the periodic movement a stream of pressurized gas is passed over the cable-like element in the tube in order to provide an advancing force on the cable-like element in the longitudinal direction of the tube. Although an improvement may be achieved as a consequence of the additional advancing force, this known insertion technique mainly has similar drawbacks as the previously discussed technique of EP-A-0091717 and EP-A-0279006.